1. Field of the Invention
This invention relates to a surface acoustic wave oscillator, and more particularly to an oscillator by which a higher-frequency signal can be obtained from an original signal by increasing the original frequency by a factor of N which is an integer greater than 1.
2. Description of the Prior Art
For obtaining a high-frequency signal, it has been known to use a surface acoustic wave (SAW) oscillator comprising a SAW resonator and an oscillator capable of generating a predetermined frequency in association with interdigital transducers (hereinafter referred to as IDT) of the SAW resonator. A signal of a desired high frequency can thus be obtained. Since the resonant frequency of the SAW resonator is determined, for example, by the line width of the IDT, the frequency which can lead to a resonance is restricted within the processing limit of the SAW resonator. Thus, if the SAW oscillator is comprised of a SAW resonator and an oscillator, the oscillating frequency can be at most about 1 GHz. If a signal with frequency higher than 1 GHz is desired, a frequency multiplier was used conventionally to obtain such a high-frequency signal.
Although it is possible to obtain desired high-frequency signals through frequency multiplication of an original signal by means of a frequency multiplier, the output from a multiplier includes many higher harmonics, and unwanted higher harmonics must be removed in order to obtain a signal with only the desired frequency. This, however, requires the use of expensive additional components such as band pass filters.